Strabismus = misalignment of the eyes, causing double vision

Physiology

• in childhood, before the eyes have established their connections with the brain, the brain reduces the signal from the dominant eye, this results in one eye they use to see and a lazy eye - if not treated the lazy eye becomes more disconnected from the brain and becomes worse = amblyopia
• Concomitant squint - due to differences in control of extra occular muscles
• paralytic quints - due to paralysis of one or more of the extra occular muscles

Definitions

• Strabismus: the eyes are misaligned
• Amblyopia: the affected eye becomes passive and has reduced function compared to the other dominant eye
• Esotropia: inward positioned squint (affected eye towards the nose)
• Exotropia: outward positioned squint (affected eye towards the ear)
• Hypertropia: upward moving affected eye
• Hypotropia: downward moving affected eye

Common types of childhood squint:

• congenital/infantile squint
  • Convergent squint is much more common than divergent.
  • The angle of the squint is often large.
  • Usually, there is no significant refractive error.
  • Cross-fixation is frequent. That is, both eyes have good vision, and the child tends to use the right eye to look to the left and the left eye to look to the right. (This is sometimes mistaken for bilateral sixth nerve palsies.)
  • Nystagmus may be present.
• Accommodative estropia
  • Generally, develops sometime between 6 months and 5 years of age, but by 3 years of age in the majority of cases.
  • May be intermittent
  • Can be fully or partially accomodative (fully or partially corrected with glasses for hypermetropia, binocular function present/not present)
• Non-accomodative estropia
  • Most commonly develops sometime between the ages of 2–5 years.
  • It may begin as an intermittent esotropia, typically when the child is tired or when concentrating on objects close by, and in time becomes constant. However, onset may be acute.
  • Hypermetropia may or may not be present, but the squint is not corrected by correction of any refractive error.
• Intermitten distance exotropia
  • It often develops between the ages of 2–5 years, but there is a significant proportion that begin later, and onset can be at any age.
  • The squint is intermittent and most commonly observed when the child is tired or in bright sunlight.
  • Visual acuity is usually good, and the incidence of refractive errors is no greater than in the general population.
  • The control of the squint may be improved by correction of any refractive error, especially myopia and astigmatism.
  • The angle of the squint is often greater when looking at distant objects, and the squint may disappear when looking at a near object or when reading.